This invention relates to electronic musical instruments and, more particularly, to an improvement of an electronic musical instrument in which musical tones are controlled by using a controlled type signal processing device such as a voltage-controlled filter and a voltage-controlled amplifier.
As is well known in the art, in controlling the tone color of a musical tone by the use of a voltage-controlled filter for instance, it is necessary to change the cut-off frequency of the voltage-controlled filter according to the tone pitch of the produced tone in order to obtain a constant tone color by unifying the relation between the harmonic components and the fundamental frequency contained in a produced tone independently of the tone pitch (fundamental frequency).
In the case where the voltage-controlled filter is employed in a conventional polyphonic tone system electronic musical instrument, a voltage-controlled filter is provided for each respective tone production channel so that each filter controls the tone source signal of one tone. Therefore, tone pitch voltages (key voltages) corresponding to the pitches of tones assigned to the filters are applied to the respective filters thereby to individually control the cut-off frequencies. However, in this arrangement, it is necessary to provide voltage-controlled filters just equal in number to the tone production channels, which increases the manufacturing cost of the electronic musical instrument.